Fuel cells have been proposed as a power source for a variety of applications including electrical vehicular power plants replacing internal combustion engines. In proton exchange membrane (PEM) type fuel cells, hydrogen is supplied to an anode of the fuel cell and oxygen is supplied as an oxidant to a cathode of the fuel cell. PEM fuel cells include a membrane electrode assembly (MEA) comprising a thin, proton transmissive, non-electrically conductive, solid polymer membrane-electrolyte having the anode on one of its faces and the cathode on the opposite face. The MEA is sandwiched between a pair of electrically conductive elements which serve as current collectors for the anode and cathode and contain appropriate channels and/or openings therein for distribution of the fuel cell's gaseous reactants over the surfaces of the respective anode and cathode catalysts. A typical PEM fuel cell and its MEA are described in commonly assigned U.S. Pat. Nos. 5,272,017 and 5,316,817 to Swathirajan et al. A plurality of individual fuel cells are commonly stacked together to form a PEM fuel cell stack.
In PEM fuel cells, hydrogen (H2) is implemented as the anode reactant and oxygen (O2) is implemented as the cathode reactant. The oxygen can be supplied in either pure form or as air (a mixture primarily comprising O2 and N2). For vehicular applications, it is desirable to use a liquid fuel, such as methanol, gasoline, diesel and the like, as the source of hydrogen for the fuel cell. Other fuels include ethanol and natural gas. Such fuels are preferential for onboard storage and a national and international infrastructure exists for supplying some such fuels. Such liquid fuels, however, must be dissociated for releasing the hydrogen content thereof. The dissociation reaction is generally accomplished in an autothermal reformer. A conventional, exemplary process is a steam/gasoline reformer where gasoline and water (steam) are ideally reacted to generate hydrogen and carbon dioxide. Additional components such as carbon monoxide may also be present.
Fuel processing systems are well known in the art. Typical fuel processing systems work by using a series of reformers to turn a hydrocarbon fuel into a hydrogen containing reformate stream. These reformers tend to be large and difficult to package. Hence, it is desirable to provide alternatives for the extraction of hydrogen.
It is known that hydrogen can be removed from a reformate stream by using a membrane coated with palladium or palladium alloy. Hydrogen separation membranes, however, tend to be unable to provide the flow of hydrogen needed by the fuel cell to maintain performance levels rivaling internal combustion engines.
Accordingly, a need exists for a fuel processing system with reduced component size and a hydrogen separation device which does not limit performance.